The caution was thrown after Williams driver Webber stopped with engine failure while holding an impressive third.

Both Raikkonen and Webber appeared able to challenge Alonso for the lead until their problems.

"The race was quite emotional from the start," said Alonso, dedicating the win to Michelin tyres chief Edouard Michelin, who died on Friday.

You can't win anything in the races, but you can lose a lot - this time Raikkonen lost a lot

Fernando Alonso

"Kimi (Raikkonen) put some pressure on me, which was quite tough, but it was good in the end.

"At Monaco you really have to keep your concentration and push to the limit all the time. It's a race that I put a cross against on my calendar at the start of the year, so now I have it. It's great for team, the Michelin and me.

"Every race is becoming more and more important for the championship fight. We are building a gap step by step.

"Basically you can't win anything in the races, but you can lose a lot. This time Raikkonen lost a lot."

Raikkonen tracked Alonso closely up to their first pit stops, with the Williams never more than a couple of seconds behind.

Schumacher spent the race in unfamiliar company

The Renault driver was able to maintain his lead thanks to stopping two laps later than the McLaren, but Raikkonen wasted no time in getting back on to his rival's tail.

Alonso's lap times dropped off dramatically early in the second stint, allowing Webber and Raikkonen's team-mate Montoya to close right up.

But the world champion speeded up as they hit heavy traffic from backmarkers halfway through the race, and only Raikkonen was able to stay with him.

Webber, though, was still within six seconds of the leaders - and still looking in contention for victory - when his engine failed as he headed into the first corner, Ste Devote, on lap 48.

The Australian pulled over to the side of the track just after the corner with flames licking from the back of the Williams.

Race officials deployed the safety car to give them time to move the Williams from a dangerous place, and all the teams pulled their drivers in for their final pit stops.

Raikkonen's race was over at the Loews hairpin on lap 50

Alonso just managed to make it out of the pits in front of Raikkonen, who appeared set for a final charge for victory before smoke began pouring from his McLaren leaving the Loews hairpin on lap 50 while the safety car was still on the track.

McLaren blamed a wiring loom that had been burnt because of heat build-up while Raikkonen was going slowly behind the safety car.

That left Montoya in second from Honda's Rubens Barrichello.

Brazilian Barrichello then lost the final podium position to Jarno Trulli after being given a drive-through penalty for speeding in the pit lane, only for the Italian to retire with five laps to go and promote Coulthard.

The Scot, who took Red Bull's first F1 podium, was not far ahead of Barrichello in the closing laps, but Barrichello had to concentrate on holding off a charge from Schumacher.

The seven-time champion closed in on his former team-mate at more than a second a lap, and was right on the Honda's tail with two laps to go, but the Brazilian was equal to the challenge and held the German off.

Schumacher had spent a frustrating race attempting to pick his way through backmarkers following his penalty for deliberately stopping on the track during qualifying.

He made up ground quickly in the opening laps after choosing to start from the pit lane with a full fuel load, but came to a halt in 16th place on lap three when he came up behind Jenson Button's Honda.

But Button was able to fend off the Ferrari only until lap 20, and Schumacher shot off to join the back of another queue.

The Ferrari had the pace to battle for victory, and combined with his need for only a single stop, that put him sixth after the safety car's intervention, which became fifth when Trulli retired.

Button spent a lonely race never threatening to break into the top 10 and eventually finished 11th.